1. Field of Invention
This invention relates to the coating of aluminum surfaces and, in particular, to the use of a certain adhesion improver in the coating process.
2. Brief Statement of the Prior Art
Cast and machined aluminum surfaces such as used for automotive wheels are exposed to extremely severe conditions during normal applications. Specifications for adhesiveness of coatings on these surfaces are accelerated and severe weathering exposure such as water immersion, and exposure to subfreezing temperatures and high pressure steam. The coatings are subjected to scratching tests and to a peel strength test. The severity of this testing has, heretofore, precluded the painting of the exposed surfaces of cast and machine aluminum wheels for original manufacturer (OEM) use.
While it is recognized that certain hydrolyzable silanes which contain functional organic groups can be used as adhesion improvers in urethane coatings and as coatings on glass fibers and minerals used as fillers in reinforced plastics, these materials have not, previously, been employed for improving the adhesion of a variety of paints to the surface of aluminum which has received a controlled oxidation pretreatment.